Sleep Stages, Cycles, And Why We Sleep

Key Takeaways

• A sleep cycle is the period of time when your brain and body rotate through sleep stages, moving from light to deep sleep to REM sleep.
• In a typical night, most people go through four to six sleep cycles, each lasting between 80 and 110 minutes.
• The four stages of sleep occur in one of two phases: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. The first three sleep stages are NREM sleep, while the fourth stage, REM sleep, is when you dream.
• High-quality sleep is essential to good physical and mental health.

Getting quality sleep can be challenging. And as we age, older adults often experience less total time sleeping, along with more disruptions to their sleep. Additionally, many sleep issues become more common for older adults, such as insomnia, sleep apnea, restless leg syndrome, sleep disorders, and stress.

How much sleep do you need each night? Adults between the ages of 18 to 64 need approximately 7 to 9 hours of sleep, while adults age 64 and older need about 7 to 8 hours per night. ^[1]Centers for Disease Control and Prevention. How much sleep do I need? Found on the internet at https://www.cdc.gov/sleep/about_sleep/how_much_sleep.html Lack of adequate sleep affects mood, thinking, and ability to learn and function. A good night’s sleep depends on the sleep cycle, which is made up of four sleep stages. Understanding the sleep cycle stages may be one way to help you catch more Zzzzs.

Why we sleep

Sleep is essential to good physical and mental health. While experts still don’t know exactly why humans need sleep, they do agree on its specific benefits, including:

• Energy conservation: Sleep is when the body conserves and restores energy. It also affects many of our internal systems, like the heart and circulatory system, hormone balance, metabolism, respiratory, and immune systems.
• Cognitive function: Sleep affects our cognitive function and impacts learning, information recall, and the forming of long-term memories. ^[5]Girardeau G, Lopes-Dos-Santos V. Brain neural patterns and the memory function of sleep. Science. 2021. Found on the internet at https://www.science.org/doi/10.1126/science.abi8370
• Brain maintenance: A study published in the journal Science found sleep allows the brain to sort and reinforce new memories in a process called consolidation, leading to long-lasting memories and better information recall. ^[5]Girardeau G, Lopes-Dos-Santos V. Brain neural patterns and the memory function of sleep. Science. 2021. Found on the internet at https://www.science.org/doi/10.1126/science.abi8370 As sleep enables the brain to sort through daily memories and activate neural networks, it serves an important role in the brain’s ability to learn and store new knowledge. Similarly, sleep deprivation can negatively impact memory and the ability to focus, make decisions, and control emotions or behavior.
• Immune support: Sleep and the body’s defense system, the immune system, affect each other in a feedback loop. Sleep disturbances can affect blood pressure, worsen inflammation, and cause an imbalance in the hormones that regulate hunger. Additionally, people who do not sleep enough are at risk for colds and other infections.

Understanding the cycles of sleep may help you figure out why your sleep may not be optimal and provides a way to help you improve your sleep hygieneⓘ Sleep hygiene refers to your sleep environment and behaviors that can affect your quality and quantity of sleep.

What are the sleep stages that make up a sleep cycle?

A sleep cycle is the period when your brain and body rotate through the four sleep stages. Typically, a full night of rest allows for four to six sleep cycles. To achieve highly restorative sleep, you need to progress easily through the four stages of sleep, as each plays an important role in maintaining your physical and cognitive health. The average sleep cycle lasts 80 to 100 minutes, at which point it starts over. ^[2]National Institutes of Health. Sleep Phases and Stages. Found on the internet at https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep

The four stages of sleep

The four stages of sleep fall into one of two phases, non-rapid eye movement (NREM) sleep and rapid eye movement (REM). NREM sleep accounts for 75 to 80% of the sleep cycle. ^[3]What Happens During Sleep? National Institute of Child Health and Human Development. April 29, 2019. Found on the internet at https://www.nichd.nih.gov/health/topics/sleep/conditioninfo/what-happens

• The first three stages of sleep, NREM sleep, is characterized by slowed brain waves, heart rate, and muscle activity.
• The final sleep stage, REM sleep, is when the body stills and the brain is active.

Each sleep cycle is made of four sleep stages and typically lasts 80 to 100 minutes.

The first stage of sleep, stage 1, lasts only one to seven minutes, beginning when you first relax to the point of drifting off to sleep. By stage 2, your body adapts by slowing down your breathing and heart rate, and your body temperature drops. In stage 3, your body, breathing, and mind are the most still, and you get the deepest sleep. These first three stages of NREM sleep take approximately 90 minutes to complete.

Stage 4 is the REM sleep stage, where your body is still while your mind is active. The REM stage is the dream stage and one that occurs before the cycle starts over. It can last anywhere from 10 minutes up to an hour before transitioning back to stage 1. ^[4]How sleep works. March 24, 2022. National Institutes of Health. Found on the internet at https://www.nhlbi.nih.gov/health/sleep/why-sleep-important

Table 1 Comparison table of the 4 stages of sleep

Sleep stages vary, but generally, this is what most people experience during their nighttime slumber.

What affects sleep stages?

Sleep patterns change through the course of our lives. Even though we need just as much sleep as before, getting a full night’s sleep can be challenging for those experiencing physical, psychological, or lifestyle changes.

• Age: As we age, we often wake up more during the night, and our deep sleep tends to decrease. The circadian rhythmⓘ Circadian rhythms are 24-hour cycles running the body’s internal clock allowing you to carry out important functions. The most well-known circadian rhythm is the sleep-wake cycle. can change as well. Chester Wu, MD, a psychiatrist and sleep specialist in Houston, Texas, said sleep issues develop for several reasons as we age. “Your circadian rhythm shifts earlier, so you may find yourself waking up earlier, and your circadian rhythm ‘flattens,’ so sleep-wake signals become weaker, causing more awakenings,” he said.
• Sleep disorders: People with sleep issues like obstructive sleep apnea (OSA) may experience daytime sleepiness as a result. OSA causes low blood oxygen levels, called hypoxemia, and sleep disturbances.
• Health conditions: Studies have made the connection between insufficient sleep and cardiovascular conditions such as coronary heart disease and heart attacks. ^[12]Zhuang Z, et al. Association of physical activity, sedentary behaviours and sleep duration with cardiovascular diseases and lipid profiles: a Mendelian randomization analysis. Lipids in Health and Disease. May 8, 2020. Found on the internet at https://lipidworld.biomedcentral.com/articles/10.1186/s12944-020-01257-z ^[13] Obesity can also affect sleep quality.Daghlas I, et al. Sleep Duration and Myocardial Infarction. Journals of the American College of Cardiology. Sept. 10, 2019. Found on the internet at https://www.sciencedirect.com/science/article/pii/S0735109719359492?via%3Dihub
• Mood disorders: Inefficient sleep can lead to or worsen mental health issues, including depression. A study published in the Journal of Affective Disorders connects the dots between sleep and depression, drawing a connection between people who get fewer than 8 hours of sleep per night and a higher rate of depression than people who get 8 or more hours. ^[10]Dong L, et al. Association between sleep duration and depression in US adults: A cross-sectional study. Journal of Affective Disorders. January 2022 Jan. Found on the internet at https://www.sciencedirect.com/science/article/pii/S016503272101034X?via%3Dihub
• Lifestyle: Many health care professionals clock long hours and work overnight, which disturbs their circadian rhythm. This disturbance causes poorer sleep quality, leading them to experience trouble falling and staying asleep. ^[9]Craig S, et al. Investigation and management of residual sleepiness in CPAP-treated patients with obstructive sleep apnoea: the European view. European Respiratory Review. May 25, 2022. Found on the internet at https://err.ersjournals.com/content/31/164/210230 Sedentary lifestyles and excessive alcohol and caffeine consumption also have a negative effect on sleep quality.

How to get better sleep

Understanding the importance of sleep serves as a great first step in improving your sleep quality. Throughout your day, there are practices you can use to promote better sleep at night. Here are some tips to improve your sleep hygiene: ^[14]Centers for Disease Control and Prevention. Tips for Better Sleep. Found on the internet at https://www.cdc.gov/sleep/about_sleep/sleep_hygiene.html

• Turn off electronics: Turn off your phone when you are getting ready for bed. Phones emit blue light that can stimulate your brain the way sunlight does.
• Invest in a new bed: Adjustable beds and quality mattresses can help improve your comfort, and help you get restful sleep.
• Keep naps short: Naps are a great way to recharge, but should only last around 30 minutes. Sleeping too long during the day can affect your nighttime sleep.
• Cut caffeine: Drink your last cup of coffee before noon.
• Reduce alcohol consumption: Although alcohol has a sedative effect and may make you feel sleepy, it actually inhibits your ability to stay asleep during the night.
• Get sunlight: Getting natural light during the day can help keep your circadian rhythm on track.
• Exercise: Staying active has many physical and emotional benefits. Getting in exercise sessions during the day can help you sleep at night.
• Manage your stress: Consider keeping a journal or seeking therapy if sleep eludes you due to stress.
• Set a sleep schedule: You’ll get better sleep if you can keep to a schedule and consistent wake time.

“As easy as it may be to justify staying out a few hours later than usual, you should aim to go to bed at the same time every night. In the morning, try to wake up at the same time, even on weekends,” said Chad Denman, MD, a sleep medicine specialist in Austin, Texas.

“While sleeping in might feel nice from time to time, it can be disruptive to your natural sleep cycle,” Denman added.

Bottom line

Getting a good night’s sleep is essential for our physical and mental health. Understanding the stages of your sleep cycles can help you manage your quality of sleep. A sleep cycle is the period of time your brain and body go through during four sleep stages. The circadian rhythm, the body’s internal sleep-wake cycle, may not be as effective as you age. A lack of sleep can have adverse effects on mood and body, and make existing conditions worse. Luckily, there are good habits you can practice to promote healthy sleep.

Have questions about this review? Email us at reviewsteam@ncoa.org.

Sources

1. Centers for Disease Control and Prevention. How much sleep do I need? Found on the internet at https://www.cdc.gov/sleep/about_sleep/how_much_sleep.html
2. National Institutes of Health. Sleep Phases and Stages. Found on the internet at https://www.nhlbi.nih.gov/health/sleep/stages-of-sleep
3. What Happens During Sleep? National Institute of Child Health and Human Development. April 29, 2019. Found on the internet at https://www.nichd.nih.gov/health/topics/sleep/conditioninfo/what-happens
4. How sleep works. March 24, 2022. National Institutes of Health. Found on the internet at https://www.nhlbi.nih.gov/health/sleep/why-sleep-important
5. Girardeau G, Lopes-Dos-Santos V. Brain neural patterns and the memory function of sleep. Science. 2021. Found on the internet at https://www.science.org/doi/10.1126/science.abi8370
6. Besedovsky L,, et al. The Sleep-Immune Crosstalk in Health and Disease. Physiological Reviews. July 1, 2019. Found on the internet at https://pubmed.ncbi.nlm.nih.gov/30920354/
7. Boivin DB, Boudreau P, Kosmadopoulos A. Disturbance of the Circadian System in Shift Work and Its Health Impact. Journal of Biological Rhythms. February 2022. Found on the internet at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8832572/
8. Yeghiazarians Y, et al. Obstructive Sleep Apnea and Cardiovascular Disease: A Scientific Statement From the American Heart Association. Circulation. July 20, 2021. Found on the internet at https://www.ahajournals.org/doi/10.1161/CIR.0000000000000988
9. Craig S, et al. Investigation and management of residual sleepiness in CPAP-treated patients with obstructive sleep apnoea: the European view. European Respiratory Review. May 25, 2022. Found on the internet at https://err.ersjournals.com/content/31/164/210230
10. Dong L, et al. Association between sleep duration and depression in US adults: A cross-sectional study. Journal of Affective Disorders. January 2022 Jan. Found on the internet at https://www.sciencedirect.com/science/article/pii/S016503272101034X?via%3Dihub
11. Brupbacher G, et al. The effects of exercise on sleep in unipolar depression: A systematic review and network meta-analysis. Sleep Medicine Reviews. 2021. Found on the internet at https://www.sciencedirect.com/science/article/pii/S108707922100037X?via%3Dihub
12. Zhuang Z, et al. Association of physical activity, sedentary behaviours and sleep duration with cardiovascular diseases and lipid profiles: a Mendelian randomization analysis. Lipids in Health and Disease. May 8, 2020. Found on the internet at https://lipidworld.biomedcentral.com/articles/10.1186/s12944-020-01257-z
13. Daghlas I, et al. Sleep Duration and Myocardial Infarction. Journals of the American College of Cardiology. Sept. 10, 2019. Found on the internet at https://www.sciencedirect.com/science/article/pii/S0735109719359492?via%3Dihub
14. Centers for Disease Control and Prevention. Tips for Better Sleep. Found on the internet at https://www.cdc.gov/sleep/about_sleep/sleep_hygiene.html

Lauren Evoy Davis Author

Lauren Evoy Davis is a health journalist with expertise in cancer and other chronic conditions. Lauren holds an MA in Journalism from American University and a BA in English from Elon University. Her work has been published by the American Society of Clinical Oncology, Legacy, Health Central, WebMD, Verywell Health, Patient Power, and Verizon.

Chester Wu Medical Reviewer

Dr. Chester Wu is board certified in Psychiatry and Sleep Medicine, training at Baylor College of Medicine and Stanford University School of Medicine, respectively. He has since established his own private practice in Houston, TX where he provides psychiatric and sleep medicine services.